1. Technical Field
This disclosure relates to fuses for semiconductor devices and more particularly, to electrical fuses with characteristics to enhance the efficiency of fuse programming.
2. Description of the Related Art
In semiconductor devices, fuses are employed in a variety of applications. For example, fuses are employed to enable redundant elements to be employed in the case of failures encountered on the semiconductor device. Some of these fuses are electrically programmable, i.e.; they are programmed by applying electric voltage or current. These electrically programmable fuses may be fabricated to include poly-silicide. Poly-silicide includes polycrystalline silicon and an overlayer of silicide, such as a metal silicide. The electrically programmable fuses typically include an appropriately shaped polysilicon layer that is silicided to obtain a poly-silicon/metal silicide stack structure.
Referring to FIG. 1, a layout (shape) of a fuse 10 is shown. Fuse 10 includes a fuse link 12, an anode 14 and a cathode 16. Current crowding takes place around a location 18 where the fuse link 12 abuts the cathode 16, when a bias is applied to set or program the fuse. When a poly-silicide fuse is programmed, the cathode is negatively biased and the anode is positively biased. The current crowding initiates electro-migration effects at the fuse link 12 resulting in further current crowding and finally for appropriate bias conditions, the poly-silicide line melts or the silicide agglomerates to result in an open circuit or a high resistance state (i.e., the fuse gets programmed) at the location 18. The effect of material migration due to, for example, electro-migration can be increased at the cathode-fuse link junction by increasing the ratio of L.sub.cathode to L.sub.fuse, as this encourages current crowding. In typical layouts, the thickness of the fuse link 12, the anode 14 and the cathode 16 are the same thickness because they are formed on the same level. Therefore, the lengths of L.sub.cathode and L.sub.fuse are determinative of the effective cross-sectional area of the fuse link/anode intersection. A polysilicon layer 20 and a silicide layer 22 as shown in FIG. 2 are provided at a uniform thickness for the fuse link 12, the anode 14 and the cathode 16. A nitride capping layer 24 is also provided over layers 20 and 22. Typical electrically programmable fuses require current flow and voltage levels at an appropriate level for a requisite amount of time to program the fuse.
Therefore, a need exists for an apparatus and method to initiate and aid mass transport processes near a fuse link/cathode intersection to reduce the programming current, voltage and time. These reductions are desirable for the electrical fuse technology to minimize energy consumption and the cost of programming fuses.